Apparatus and methods for microchannel cooling of semiconductor integrated circuit packages

ABSTRACT

Apparatus and methods are provided for microchannel cooling of electronic devices such as IC chips, which enable efficient and low operating pressure microchannel cooling of high power density electronic devices having a non-uniform power density distribution, which are mounted face down on a package substrate. For example, integrated microchannel cooler devices (or microchannel heat sink devices) for cooling IC chips are designed to provide uniform flow and distribution of coolant fluid and minimize pressure drops along coolant flow paths, as well as provide variable localized cooling capabilities for high power density regions (or “hot spots”) of IC chips with higher than average power densities.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to apparatus and methods forcooling electronic devices. More specifically, the present inventionrelates to microchannel cooling apparatus and methods which provideimproved fluid distribution and flow mechanisms for efficient cooling ofsemiconductor integrated circuit (IC) chip packages, as well asincreased localized cooling capabilities for high power density regionsof semiconductor chips.

BACKGROUND

In the design and manufacture of semiconductor IC (integrated circuit)chip packages and modules, it is imperative to implement mechanisms thatcan effectively remove heat generated by IC chip devices (such asmicroprocessors) to ensure continued reliable operation of such devices.Indeed, heat removal is particularly important for computer processorchips that are disposed in SCM (single chip modules) or MCMs (multichipmodules), for example, which can generate significant amounts of heat.The ability to efficiently remove heat becomes increasing problematic aschip geometries are scaled down and operating speeds are increased,resulting in increased power density. Although IC chip modules are beingcontinually designed to operate at higher clock frequencies, increasedsystem performance is becoming limited primarily by the ability toeffectively remove heat from such IC chip modules.

There are various heat removal techniques that have been developed forcooling semiconductor IC packages/modules and other electronic devices.For example, microchannel cooling apparatus and methods have beenproposed for cooling electronic devices such as IC chips, MCMs, diodelaser arrays, and other electro-optic devices under conditions ofincreased heat flux (power/unit area) or high power densities (e.g.,˜800 W/cm²).

FIGS. 1A and 1B are schematic diagrams that illustrate a conventionalmicrochannel cooling apparatus, such as described in U.S. Pat. No.4,573,067, wherein FIG. 1B illustrates a cross-section view of FIG. 1Aalong the line 1B. As shown, a semiconductor chip (10) includes circuitsthat are formed in a front surface region (11) of the semiconductor chip(10). A rear surface of the chip (10) is processed to form a recessedregion (12) and a plurality of parallel, microscopic heat conductingfins (14) rising from the recessed region (12), which define a pluralityof channels (13). A transparent cover (15) engages the surface of chip(10) and the tops of the fins (14) thereby defining a chamber for theflow of a coolant through the channels (13) between the input and outputports (16) and (17) in the transparent cover (15), wherein heat removalis achieved by thermal contact between the fins (14) and the coolantfluid that flows through the channels (13).

There are a number of disadvantages associated with the coolingapparatus depicted in FIGS. 1A and 1B. For instance, such design resultsin significant pressure drops and non-uniform flow distribution due to,e.g., the use of one heat exchanger zone (with long channel length)between the input port (16) and the output port (17), and having aninput port (16) and output port (17) with a cross sectional area that issmaller than the total microchannel cross sectional area. Furthermore,the process of forming the fins (14) and channels (13) directly in thenon-active surface of the IC chip (10) can result in reduced yield forthe chips (10), which is not desirable especially for expensive chipssuch as microprocessors. Indeed, if the microchannel cooler fails orleaks, the chip, which is much more expensive than the cooler in thecase of a high performance processor, is lost along with themicrochannel cooler.

FIGS. 2A˜2C schematically illustrate another conventional microchannelcooling apparatus, such as described in U.S. Pat. No. 5,998,240. FIG. 2Adepicts a silicon chip (20) having a region containing a plurality ofmicrochannels (21) formed therein, which comprise a plurality ofclose-ended slots or grooves of generally rectangular cross-section. Asdepicted in FIG. 2B, the chip (20) sits on a ceramic frame (22) thatincludes three generally rectangular coolant manifolds (23), (24) and(25). The center manifold (24) comprises a coolant input manifold havinga coolant inlet port (27) formed at one end, while the two outermanifolds (23) and (25) comprise output manifolds and include coolantoutlet ports (26) and (28) at the opposite end from the inlet port (27).The die (20) is oriented with respect to the ceramic substrate (22) suchthat the microchannels (21) are orthogonal to the manifolds (23), (24)and (25). As depicted in FIG. 2C, the chip (20) and the ceramicsubstrate (22) are mounted on a ground plane (29) having two coolantoutput ducts (29 a) and a single coolant input duct (29 a), wherein theliquid coolant flow direction is shown by the arrows.

There are a number of disadvantages with the conventional microchannelcooling apparatus depicted in FIGS. 2A˜2C. For instance, if thesubstrate (22) comprising the manifold channels (23, 24, 25) wasfabricated using Silicon, the substrate would be weak and likely breakduring fabrication due to the formation of the multiple channels throughthe substrate with sharp-edge corners. Moreover, such design results insignificant pressure drops and non-uniform flow distribution, whichresult from (i) the input and output ports (26, 27, 28) having a smallercross sectional area than the total microchannel cross sectional area,(ii) the manifolds (23, 24, 25) having grooves which are of constantcross section feeding the microchannels (21) and (iii) having themicrochannels (21) continue below the inlet manifold groove (24) whentwo outlet manifold grooves (23, 25) are used.

FIGS. 3A and 3B are schematic diagrams illustrating other conventionalmicrochannel cooling structures, such as described in U.S. Pat. No.5,218,515. FIG. 3A illustrates a cut-away perspective view of anintegrated circuit module (30), which includes an IC chip (31) havingsolder bump bonding sites (32) along a front (active) surface (31 a) ofthe chip (31). A back (non-active) surface (31 b) of the chip (31) isthermally bonded to a microchannel structure (33). A plurality ofmicrochannels (33 a) are formed in the microchannel structure (33). Acover manifold (34) is bonded to the microchannel structure (33). Inputand output coolant delivery channels (34 a) and (34 b) are cut or formedin the cover manifold (34) as illustrated.

FIG. 3B illustrates a coolant supply manifold (35) which is used tosupply coolant for a multi-chip module (MCM) package comprising an arrayof the microchannel cooled IC modules (30) mounted face down on a commonsubstrate or circuit board. The coolant supply manifold (35) includes aplurality of coolant supply channels (e.g. (36), (37), (38) and (39)),wherein channels (36) and (38) are higher pressure channels whilechannels (37) and (39) are lower pressure channels. The manifold (35) isadapted for placement over a printed wiring card so that, e.g., theopenings (36 a) and (37 a) in respective coolant supply channels (36)and (37) mate with the openings (34 a) and (34 b) in the individualintegrated circuit modules (30) on the circuit board. Elastomer sealsare used to couple the coolant supply manifold (35) with the integratedcircuit modules (30).

There are disadvantages associated with the microchannel coolingapparatus depicted in FIGS. 3A and 3B. For instance, the microchannelcoolers (30) are formed with one heat exchanger zone (between the inputand output manifold channels (34 a, 34 b)), which can result insignificant pressure drops of fluid flow along the microchannels (33 a).Moreover, if a cover manifold (34) was formed with multiple coolantdelivery channels (e.g., 34 a) for multiple heat exchanger zones toreduce the pressure drop, the cover manifold (34) would be fragile andlikely to break during fabrication, thereby reducing manufacturingyield.

Furthermore, the coolant supply manifold (35) design of FIG. 3B canresult in large pressure drops and significant non-uniform flowdistribution due to the channels, which feed a given column of fourmicrochannel inlets, having a constant cross-sectional area. Forinstance, as depicted in FIG. 3B, the supply channel (36) feeds coolantfluid to four coolant delivery manifolds (34 a) of module (30) (FIG. 3A)via the four openings (36 a). Assume V, ΔP, and Q are the velocity,differential pressure and total flow in the last manifold segment, i.e.,between the bottom two microchannel inlets, then the segment above willdesirably have velocity 2V, and total flow 2Q. This higher velocity willresult in a segment pressure drop equal to ˜2ΔP if the flow is laminarand ˜4ΔP if the flow is turbulent (given the linear dependency betweenflow and pressure drop when the flow is laminar, but quadraticdependency when the flow is turbulent). Thus, for a manifold channelwith constant cross-section feeding four microchannel inlets, we canexpect a total manifold channel pressure drop of ˜10 ΔP if the flow islaminar, and ˜30 ΔP if the flow is turbulent. This large pressure dropwill induce flow variations within the different microfin sections thatcan not be compensated with a return line, also with constantcross-section but with reverse orientation relative to the inlet line.Since the manifold channel has to carry significantly larger water flowthan a given microchannel, both velocity and cross-section will behigher, therefore, it is easy to expect (or difficult to avoid) having a10× increase in the Reynolds number between these two sections. For lowcooling capability, like less than 50 W/cm², the water flow requirementsare low, and it is possible to have both manifold channels andmicrochannels with laminar flow regimes, but at high flows this is notpossible since the microchannels will require flow regimes with Reynoldsnumber in the 100-200 range, then, the flow regime in the manifoldchannel will not be laminar.

Another disadvantage associated with the conventional designs discussedabove is that no mechanisms are provided for efficient heat removal forIC chips, such as processors, that have “hot spot” regions, i.e.,regions of the chip which can have a heat flux (power/unit area) that issignificantly greater than the average heat flux of the chip, whichcould result in temperatures ˜20° C. hotter than the average chiptemperature. Indeed, one thermal solution which is designed forefficiently removing heat that is generated due to average chip powerdensity, may not be adequate for removing heat at “hot spot” regions ofthe chip, which can result in failure of the chip devices in or near the“hot spot” region.

SUMMARY OF THE INVENTION

Exemplary embodiments of the invention generally include apparatus andmethods for cooling of electronic devices and, in particular, apparatusand methods for microchannel cooling of IC (integrated circuit) chipshaving a non-uniform power density distribution, which are mounted facedown on a package substrate. More specifically exemplary embodiments ofthe invention include microchannel cooling apparatus and methods whichimplement mechanisms to provide variable localized cooling capabilitiesfor high power density regions (or “hot spots”) of semiconductor chipswith higher than average power densities to locally increase the coolingcapacity for “hot spot” areas on an IC chip with higher than averagepower densities.

For example, in one exemplary embodiment of the invention, an integratedmicrochannel cooler device is provided for cooling an IC (integratedcircuit) chip having a non-uniform power map. The microchannel coolerdevice comprises a plurality of alternating input and output manifoldsthat extend in a same direction within the integrated cooler device anda plurality of heat exchanger zones. Each heat exchanger zone comprisesa plurality of thermal microfins which define a microchannel pattern ofmicrochannels which extend between an adjacent input and output manifoldto provide fluid flow paths between the adjacent input and outputmanifold. The microchannel pattern of one or more of the heat exchangerzones is varied to provide a heat transfer performance that correspondsto an expected power map of the IC chip. The input and output manifoldsand microchannel patterns of the heat exchanger zones are structured soas to provide an average fluid velocity in a region of a heat exchangerzone that corresponds to an expected hot spot region of the IC chip,which is substantially the same as, or at least within about 50% of, anaverage fluid velocity in other regions of the heat exchanger zone thatdo not correspond to an expected hot spot region of the IC chip.

In another exemplary embodiment of the invention, at least one inputmanifold of the integrated microchannel cooler device is arranged toalign with an expected hot spot region of the IC chip. In anotherembodiment, the microchannel pattern of one or more of the heatexchanger zones is varied locally to provide a heat transfer performancethat corresponds to local variations of the expected power map of the ICchip. In yet another embodiment, at least one heat exchanger zonecomprises a first pattern of microchannels that provides a heat transferperformance sufficient for an expected average power density of the ICchip and a second pattern of microchannels that is disposed tocorrespond to an expected hot spot region of the IC chip, wherein thesecond pattern of microchannels provides a heat transfer performancesufficient for an expected greater than average power density of the hotspot.

These and other exemplary embodiments, aspects, features, and advantagesof the present invention will become apparent from the followingdetailed description of the preferred embodiments, which is to be readin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic diagrams that illustrate a conventionalapparatus for microchannel cooling an IC chip.

FIGS. 2A-2C are schematic diagrams that illustrate another conventionalapparatus for microchannel cooling an IC chip.

FIGS. 3A and 3B are schematic diagrams that illustrate conventionalapparatus for microchannel cooling IC chips for an MCM (multi-chipmodule).

FIGS. 4A-4D are exemplary schematic diagrams that illustrate a manifoldplate and method for fabricating the manifold plate, according to anexemplary embodiment of the invention.

FIGS. 5A˜5B are schematic diagrams that illustrate a microchannel plateaccording to an exemplary embodiment of the invention, which can bejoined with the exemplary manifold plate of FIGS. 4A-4D for constructingan integrated microchannel cooler device according to one exemplaryembodiment of the invention.

FIG. 6 is schematic detailed illustration of a portion of a manifoldstructure according to an exemplary embodiment of the invention.

FIG. 7 is a schematic cross-sectional diagram illustrating an apparatusfor microchannel cooling a semiconductor chip according to an exemplaryembodiment of the invention.

FIGS. 8A˜8B are schematic cross-sectional diagrams illustrating anapparatus for microchannel cooling a semiconductor chip according toanother exemplary embodiment of the invention.

FIG. 9A˜9C are schematic diagrams of perspective views that illustratean apparatus for microchannel cooling a semiconductor chip according toanother exemplary embodiment of the invention.

FIG. 10 is a schematic plan view of a fluid distribution manifold deviceaccording to an exemplary embodiment of the invention.

FIG. 11 is a schematic plan view of a fluid distribution manifold deviceaccording to another exemplary embodiment of the invention.

FIG. 12 is a diagram that schematically illustrates a method forproviding a locally increased cooling capacity for a “hot spot” regionof a chip according to an exemplary embodiment of the invention.

FIG. 13 is a diagram that schematically illustrates a method forproviding a locally increased cooling capacity for a “hot spot” regionof a chip according to another exemplary embodiment of the invention.

FIG. 14 is a diagram that schematically illustrates a method forproviding a locally increased cooling capacity for a “hot spot” regionof a chip according to yet another exemplary embodiment of theinvention.

FIG. 15 is a diagram that schematically illustrates a method forproviding a locally increased cooling capacity for a “hot spot” regionof a chip according to another exemplary embodiment of the invention.

FIG. 16 is a diagram that schematically illustrates a method forproviding a locally increased cooling capacity for a “hot spot” regionof a chip according to yet another exemplary embodiment of theinvention.

FIGS. 17A and 17B are schematic diagrams that illustrate differentmicrofin patterns that can be implemented in a microchannel coolerdevice, according to exemplary embodiments of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention as described herein generallyinclude apparatus and methods for cooling of electronic devices and, inparticular, apparatus and methods for microchannel cooling of IC(integrated circuit) chips mounted face down on a package substrate,where the IC chips may have a non-uniform power density distribution. Ingeneral, an apparatus for microchannel cooling an electronic deviceaccording to one exemplary embodiment of the invention comprises anintegrated microchannel cooler device (or microchannel heat sink) thatis thermally bonded to a non-active surface of an IC chip mounted facedown on a package substrate, and a fluid distribution manifold device,which is removably coupled to the integrated microchannel device via amechanically compliant gasket, to deliver coolant fluid to/from theintegrated microchannel device. Microchannel cooling apparatus andmethods according to various exemplary embodiments as described hereinimplement fluid distribution and flow mechanisms which foster uniformflow of coolant fluid and which prevent/mitigate reduction of pressureof the coolant fluid along the coolant flow paths, to thereby providehigh cooling rate capability and efficiency for cooling electronicdevices such as semiconductor integrated circuit (IC) chippackages/modules. In other embodiments, microchannel cooling apparatusand methods implement mechanisms that provide variable localized coolingcapabilities for high power density regions (or “hot spots”) ofsemiconductor chips to locally increase the cooling capacity at areas onan IC chip having higher than average power densities.

More specifically, exemplary embodiments of the invention includevarious frameworks/architectures for integrated microchannel coolerdevices that can be thermally bonded to IC chips, which are designed tooptimize the distribution and flow of coolant fluid for efficient heatremoval. For example, in one exemplary embodiment of the invention, anintegrated microchannel cooler device comprises a microchannel platehaving a plurality of microchannels defined by microfins formed in onesurface of the microchannel plate, and a manifold plate (or manifoldcover), which is bonded to the microchannel plate, having a plurality ofcoolant supply/return manifolds. In another exemplary embodiment of theinvention, an integrated microchannel cooler device comprises a singleplate that is constructed with both microchannels and supply/returnmanifolds structures. In all such embodiments, an integratedmicrochannel cooler device includes supply/return manifolds andmicrochannels/microfins that are structured, patterned, dimensionedand/or arranged in a manner that minimizes pressure drop and increasesuniformity of fluid flow and distribution along coolant flow pathsand/or enables variable localized cooling for hot spot regions of achip.

An integrated microchannel cooler device according to one exemplaryembodiment of the invention will now be discussed in detail withreference to the exemplary embodiments of FIGS. 4A˜4D and FIGS. 5A˜5B,for example. In particular, FIGS. 4A˜4D are schematic diagramsillustrating a manifold plate (40) according to an exemplary embodimentof the invention, which can be bonded to a corresponding microchannelplate (50) as depicted in the exemplary schematic diagrams of FIGS.5A-5B, to form an integrated microchannel cooler device.

More specifically, with initial reference to the illustrative views ofFIGS. 4A˜4D, an exemplary manifold plate (40) comprises a planarsubstrate (41) having a plurality of fluid manifolds (M1˜M7) (or denotedgenerally, Mi) formed therein. Each fluid manifold (M1˜M7) comprises acorresponding manifold channel (C1˜C7) (or more generally, Ci) formed inone surface (S2) of the substrate (41) and a correspondingpattern/series of fluid vias (V1˜V7) (or more generally, Vi) having aplurality of fluid vias (v) that form openings which extend from asurface (S1) (which is opposite the surface (S2)) to various pointsalong the corresponding manifold channels (C1˜C7). As explained below,the fluid manifolds (Mi) are structured, patterned, dimensioned and/orarranged in a manner that enables the manifold plate (40) to provide auniform flow distribution and reduce overall system pressure drop, aswell as maintain the structural integrity of the manifold plate toprevent breakage during manufacturing.

More specifically, FIG. 4A is a schematic plan view of the manifoldplate (40) at one stage of production in which the plurality ofpatterns/series of fluid vias (V1˜V7) are formed in one surface (S1) ofthe planar substrate (41), which is the bottom surface of the substrate(41) in the illustrative view. In other words, FIG. 4A depicts thepatterns of vias (V1˜V7) as viewed from a top surface (S2) of thesubstrate (41) which is opposite the bottom surface (S1) in which thevias (v) are formed. FIG. 4B is a schematic cross-sectional view of aportion of the substrate (41) along line AA of FIG. 4A, whichillustrates the substrate (41) having a thickness (T) and the vias (v)being formed to a depth (d1) below the substrate surface (S1) (i.e., thevias are not formed entirely through the substrate (40)). In oneexemplary embodiment of the invention in which the substrate (41) isformed of silicon (Si), the fluid vias can be formed using a deep Sietching method to etch the fluid vias partially through the substrate(41). In particular, in one exemplary embodiment, for a typical siliconwafer substrate having a thickness, T, of 0.75 mm, the fluid vias (v)can be formed to a depth of d₁=0.50 mm. Further, the fluid vias can becircular holes with a diameter of about 450 microns. It is to be notedthat although circular holes are shown in the exemplary embodiment, thefluid vias may be formed with other shapes, preferably with roundedcorners (as compared to shapes with sharp corners that act as stressconcentration sites which can increase the possibility of breakage ofthe components during manufacturing).

As depicted in the exemplary embodiment of FIG. 4A, via patterns (V1)and (V7) comprise a series of circular openings that are arranged in alinear pattern, and the via patterns (V2)˜(V6) each comprise a series ofcircular openings arranged in a zig-zag pattern. As explained below, afabrication method in which the manifolds are constructed by forming aseries of circular openings in a zig-zag pattern reduces the potentialof wafer (or substrate) breakage during manufacturing of the manifoldplate, when forming multiple manifolds to define multiple heat exchangerzones.

Each pattern/series of fluid vias (Vi) comprises a plurality of openingsthat serve as fluid inlets/outlets to a corresponding input/outputmanifold channel (Ci) that is formed on the surface (S2) of thesubstrate (41) opposite the surface (S1) in which the patterns of fluidvias (Vi) are formed. For example, FIG. 4C illustrates a schematic planview of the exemplary manifold plate (40) at another stage of productionin which manifold channels (C1˜C7) are formed in the surface (S2) of thesubstrate (41), wherein each manifold channel (C1˜C7) comprises acontinuous cavity that is patterned and recessed to a depth that issufficient to connect to each fluid via (v) of a corresponding patternof fluid vias (V1˜V7). More specifically, FIG. 4D is a schematiccross-sectional view of a portion of the substrate (41) along line BB ofFIG. 4C, which illustrates a channel segment of the manifold channel C2,which is formed between two vias (v) by etching a recess between thevias (v) in the substrate (41) to a sufficient depth, d₂, below thesurface (S2) of the substrate (41) to connect with the fluid vias (v).Continuing with the exemplary embodiment described with respect to FIG.4B wherein the substrate (41) of the manifold plate (40) is formed ofsilicon, the manifold channels (Ci) can be formed using a deep Sietching process to etch the recesses to a depth of d_(2=0.25) mm.

Furthermore, in an exemplary embodiment of the invention, the manifolds(Mi) comprise manifold channels (Ci) that are formed having a variablecross-sectional area. For instance, FIG. 6 is schematic detailed view ofthe manifold structure for a portion of the fluid manifold (M2) inregion (43) as depicted in FIG. 4C. In the exemplary view of FIG. 6, thechannel segments (44) between the fluid vias (v) form tapered recesseswhich taper down away from the fluid vias (v) to decrease the channelcross-sectional area. Details of the exemplary manifold structure arefurther depicted in FIG. 9A, which depicts a three-dimensionalperspective view of a manifold channel (91) having a zig-zag pattern,which is formed in a manifold plate (90). In particular, FIG. 9A depictsa plurality of fluid vias (v) that form openings to a manifold channel(92), wherein the manifold channel (92) is patterned such that channelsegments (93) between two fluid vias (v) form tapered recesses.

Advantageously, the tapered manifold channel widths help to minimizedynamic pressure drop along the channels by maintaining the flowvelocity of the coolant fluid relatively constant. More specifically,varying the cross-sectional area of the manifold channels (Ci) providesa means for reducing dynamic pressure drop along the manifold channels(Ci) and thereby enabling the manifold channels (Ci) to uniformlydistribute the flow of coolant fluid to/from microchannel inlet/outletsthat are disposed along the manifold channels (Ci).

FIGS. 5A and 5B are schematic diagrams illustrating a microchannel plateaccording to an exemplary embodiment of the invention. Morespecifically, FIG. 5A is a schematic plan view of a microchannel plate(50) which is compatible for use with the exemplary manifold plate (40)of FIG. 4C, for example. In FIG. 5A, the microchannel plate (50)comprises a substrate (51) (e.g., Si substrate). The substrate (51)comprises a region (52) that is etched (using deep Si etching or othersuitable techniques known to those of ordinary skill in the art) to forma plurality of parallel thermal microfins (53) which definemicrochannels (54) (see FIG. 5B) that extend in the same directionacross the region (52). The microchannels (54) comprise a plurality ofopen-ended slots or grooves of generally rectangular cross-section.

In the exemplary embodiment of FIG. 5A, the microfins (53) are notcontinuous across the region (52), but are interrupted/discontinuous insuch as way as to form recessed regions (R1˜R7) which correspond to, andare aligned with, the manifold channels C1˜C7 (FIG. 4C) when themanifold plate (40) is bonded to the microchannel plate (50) to form anintegrated microchannel cooler device. By way of example, FIG. 5B is adetailed illustration of a portion (55) of the microchannel plate (50)of FIG. 5A, wherein the microfins (53) are discontinuous across therecess region (R2) which corresponds to (aligned with) the manifoldchannel (M2) of manifold plate (40) (e.g., portion (43) as depicted inFIG. 6). The recessed regions (R1˜R7) act as manifolds in conjunctionwith the corresponding manifold channels (C1˜C7) of the manifold plate(40) to increase the area available for the distribution of fluid thatflows from the fluid vias (v) to the microchannel (for inlet manifolds)and for the distribution of fluid that flows from the microchannels tothe fluid vias (for outlet manifolds). For instance, the portion (43) ofthe manifold plate depicted in FIG. 6 illustrates a portion of amanifold channel that corresponds to, and can be aligned with, theportion of the recessed region R2 depicted in FIG. 5B. In this regard,the combined area of the manifold channel and recessed regions providesan increased area for fluid flow and distribution.

Moreover, as depicted in FIG. 6, for example, the channel segments (44)of the manifold channel between the fluid vias (v) have varyingcross-sectional areas for purposes of reducing pressure drop. Morespecifically, as depicted in the exemplary embodiments of FIGS. 5B and6, the channel segments (44) between the input fluid vias (v) ofmanifold channel (C2) and corresponding portions of the recessed regions(R2) are tapered down away from input fluid vias (v), so as to reducethe cross-sectional area along the coolant path. This results in reducedpressure drop and maintaining the velocity of fluid flow constant, so asto uniformly feed coolant into the microchannels that are disposed alongthe channel segments.

Furthermore, with the exemplary embodiment depicted in FIG. 5B, the endportion of the microfins (53) along the recessed region (e.g., R2 asshown in FIG. 5B) can be formed with rounded or tapered edges to providea further reduction in overall system pressure drop. Indeed, the roundedor tapered edges of the microfins (53) results in microchannels (54)having rounded inlet/outlet corners, which reduces the flow resistanceby smoothing the incoming/outgoing flow stream.

In one exemplary embodiment of the invention, assume the microfins (53)are formed having a width, W_(F)=90 micron, and define the microchannels(54) having a channel width W_(C)=60 micron and channel depth of 250micron deep. Further assume that a vertical spacing (Vs) between twoadjacent fluid vias (v) (as indicated in FIG. 6) is 0.6 mm, and each via(v) provides coolant to/from a series of microchannels to both the leftand right side of the adjacent manifold channel segments (44).Therefore, in this exemplary embodiment, the total cross-sectional areaof the microchannels that a single fluid via (v) provides coolantto/from is 1.2 mm×0.25 mm×60%=0.18 mm² (wherein 1.2 mm=2 Vs and 0.25 mmis the depth of the microchannels. Further assuming (as mentionedpreviously) that diameter of the fluid via (v) is 0.450 mm (whichcorresponds to a cross-sectional area of 0.16 mm²), each manifoldchannel segment (44) has an initial cross-sectional area of0.450×0.25=0.11 mm² and provides fluid flow to/from microchannels (54)having a cross-sectional area of 0.09 mm².

It is to be appreciated that recessed regions (R) to which the manifoldchannels (C) are aligned also provide additional cross-sectional areafor fluid flow. This additional area is provided to reduce the pressuredrop caused by the changing direction of the fluid flow as well as thechanging geometry of the channel. The microchannels will have more wetperimeter per unit of area than the feeding via (v) and, consequently,there will be an increased pressure drop. The additional volumeinterconnecting these two structures will allow the fluid flow to find apath of low resistance away from the walls. With a smaller volume, thepressure drop penalty will increase due to the wall friction. Asdescribed above, the cross-sectional area of the fluid via (v), theinitial cross-sectional area of each manifold channel segment, and thetotal cross-sectional area of the microchannels to which fluid isprovided to or from are all within 25% of their average value.

As noted above, an integrated microchannel cooler device can be formedwith the exemplary manifold plate (40) and microchannel plate (50) bybonding the surface (S2) of the manifold plate (40) to the microchannelplate (50) such that the manifold channels (Ci) are aligned with andface the corresponding recessed regions (Ri). More specifically, anintegrated microchannel cooler device having an overall size of 20×20 mmwith six heat exchanger zones formed between alternating input andoutput manifolds, as indicated by “I” and “O” in FIG. 4C, and having themanifold/microfin/microchannel dimensions set forth and discussed above,can be constructed using the exemplary plates (40) and (50). Exemplarymethods for forming integrated cooler devices and packaging such deviceswith IC chips will be further explained below with reference to FIGS. 7and 8, for example.

It is to be appreciated that integrated microchannel cooler devicesaccording to exemplary embodiments of the invention provide efficientand low operating pressure microchannel cooler frameworks which enableeffective cooling for electronic devices having very high powerdensities, and which can be readily manufactured and integrated with thechip packaging, for example. More specifically, various exemplaryembodiments of an integrated microchannel cooler devices according tothe invention are designed with fluid manifolds, microfins andmicrochannels that are structured, patterned, dimensioned and/orarranged in a manner, for example, to provide (i) a uniform distributionand flow of coolant fluid and an overall reduction in the systempressure drop, (ii) an increase in manufacturing yields when fabricatinga cooler device; and (iii) ease of integration with chip packaging.

More specifically, by way of example, with respect to ease ofintegration with chip packaging, the use of fluid vias on the backsurface of the manifold chip to input/output coolant fluid to/from theintegrated microchannel cooler device enables the microchannel coolerdevice to be dimensioned such that is does not extend significantlybeyond the area of the chip being cooled. This is especiallyadvantageous for MCMs, where chips are mounted very close to each other.Moreover, as explained further below, by forming themicrofin/microchannel structures in a separate layer (as opposed toforming such structures in the non-active surface of the chip to becooled), an individual microchannel cooler device can be firstconstructed and tested, and then thermally bonded to the chips in amanner that enables any yield loss during the cooler fabrication not toresult in yield loss of the assembled chip and integrated cooler.

Moreover, with respect to increasing manufacturing yield, the fluidmanifolds are designed/structured in such as way as to maintain thestructural integrity of the substrate in which the manifolds are formedand minimize the potential of breakage of the substrate. Indeed, asexplained with reference to the exemplary manifold plate (40), themanifolds (Mi) are not formed with continuous elongated slots forproviding the coolant flow (as in conventional designs), but rather witha series of circular openings, or openings with rounded corners,arranged in a zig-zag pattern, to reduce wafer cracking duringmanufacturing, and with manifold channels formed between the circularopenings on the plate surface that faces the microchannels. Thesemanifold structures reduce the potential of wafer breakage by usingcircular openings to minimize stress concentrations which can serve ascrack nucleation sites, minimizing the total cavity area of the channelmanifolds by using the recessed regions of the microchannel pattern toact as a manifold in conjunction with the manifold channels, and avoidaligning the cavities along the (100) Si cleavage planes.

Furthermore, integrated microchannel cooler devices according toexemplary embodiments of the invention may implement various mechanismsfor achieving uniformity of the distribution and flow of coolant fluidand an overall reduction in the system pressure drop. For instance, onemethod that is implemented for reducing the pressure drop is subdividingthe coolant flow into multiple heat exchanger zones so that the flowpaths through the microchannels are short. More specifically, by way ofexample, the exemplary manifold and microchannel plate embodimentsdiscussed above, provide multiple input and output fluid manifolds (Mi)for defining multiple heat exchanger zones. Indeed, as depicted in theexemplary microchannel plate (50) of FIG. 5A and manifold plate (40) inFIG. 4C, six heat exchanger zones are defined by alternating input andoutput manifolds, wherein each input manifold (M2, M4 and M6) feeds twozones of microchannels that end at output manifolds (M1, M3, M5 and M7).Further, the ziz-zag manifold structures enable the formation ofmultiple manifolds while maintaining the structural integrity of thechip.

Another method for reducing pressure drop is to design the manifoldssuch that each manifold channel has an initial, or final,cross-sectional area that is at least equal to a total cross-sectionalarea of all microchannels that receive coolant fluid from the manifoldchannel, or that supply coolant fluid to the manifold channel. Forinstance, in the exemplary embodiments of FIG. 4C and FIG. 5A, the inputmanifold channels C2, C4 and C6 each feed two zones of microchannels. Assuch, the initial cross-sectional area of each of the input manifoldchannels should be at least as large as the sum of the microchannelcross-sections that are fed by such channels. Moreover, the outputmanifold channels C3 and C5 each received coolant fluid from 2 zones ofmicrochannels. As such, the final cross-sectional area of outputmanifold channels C3 and C5 should be at least as large as the sum ofthe microchannel cross-sections that feed such manifold channels (or, inthe exemplary embodiment, the cross-sectional area of each manifoldchannel C2˜C6 should be the same). On the other hand, the outputmanifold channels C1 and C7 are each fed by one zone of microchannels.As such, the final cross-sectional area of each output manifold channelC1 and C7 should be no less than one-half the initial cross-sectionalarea of the input manifold channels (M2 and M6).

Similarly, another method for reducing pressure drop is to design themanifolds such that the fluid vias for each manifold have a totalcross-sectional area that is at least equal to the total cross-sectionalarea of all microchannels that receive coolant fluid supplied throughthe fluid vias or that supply coolant fluid which is output from thefluid vias. For instance, the fluid vias for via pattern V4 should havea total cross-sectional area at least equal to the sum of thecross-sectional area of the microchannels that are fed by thecorresponding manifold channel C4.

Moreover, as noted above, another manifold design feature for reducingpressure drop is to vary the cross-sectional area of the manifoldchannels to uniformly feed coolant fluid to the microchannels. Forinstance, as depicted in the exemplary embodiments of FIGS. 5B and 6,the channel segments (44) between the input fluid vias (v) of manifoldchannel (C2) and corresponding portions of the recessed regions (R2) aretapered down away from input fluid vias (v), to as to reduce thecross-sectional area along the coolant path. This results in reducedpressure drop and maintaining the velocity of fluid flow constant, so asto uniformly feed coolant into the microchannels that are disposed alongthe channel segments. Moreover, the pressure drop can be further reducedby rounding or tapering the microchannel inlet corners which reduces theflow resistance by smoothing the incoming flow.

Overall, an integrated microchannel cooler device according to theinvention, which is formed from the exemplary manifold and microchannelplates (40) and (50), provides a multi-heat exchanger zone structure inwhich all the heat exchanger zones are connected in parallel, whichmeans that the heat exchanger zones are uniformly designed (e.g., themicrochannel pattern is the same (continues channels with same pitch) inall heat exchanger zones, and the alternating input and output manifoldsare equally spaced so that microchannel lengths are substantially thesame for all heat exchanger zones) to operate with the same pressuredrop between the inlet and outlet manifolds, and the manifolds aredesigned with variable cross-sectional areas so as to ensure that for agiven heat exchanger zone, there is a uniform distribution of coolantacross the heat exchanger zone. In this manner, the integratedmicrochannel cooler can be designed with a sufficient number of parallelheat exchanger zones and flow pressures based on an expected averagepower density of a chip, to provide a flow per unit width and pressuredrop per unit length that is sufficient to effectively cool the chipwith such average power density.

FIG. 7 is a schematic diagram of an apparatus for cooling an asemiconductor chip according to an exemplary embodiment of theinvention. More specifically, FIG. 7 schematically illustrates across-sectional side-view of a semiconductor package (70) according toan exemplary embodiment of the invention, which comprises an integratedmicrochannel cooler device (71) that is thermally coupled to the back(non-active) surface of a semiconductor chip (72) (e.g., processor chip)via a thermal bond (B2). The active surface of the chip (72) comprises aplurality of solder balls (C4 s) for flip-chip bonding to a packagesubstrate.

The microchannel cooler device (71) comprises a microchannel plate (74)and manifold plate (75) that are joined via a bond (B 1), and the plates(74) and (75) can have manifold and microchannel structures similar tothose discussed above with respect to FIGS. 4A-4D and 5A-5B. In thisregard, the exemplary embodiment of FIG. 7 may be considered across-sectional view along a longitudinal line which: (i) extends in adirection parallel to a zig-zag shaped fluid manifold structure formedin the manifold plate (75) and orthogonal to a plurality of thermalmicrofins (76) and microchannels (77) of the microchannel plate (74);and which (ii) passes through the center of each of a plurality of fluidvias (v) formed on one side of the zig-zag shaped fluid manifoldstructure. As depicted in FIG. 7, the fluid vias (v) form openings atpoints along the manifold channel (C), and the microchannel plate (74)comprises a plurality of regions (R) in which the thermal microfins (76)are discontinued. The plurality of thermal microfins (76) and channels(77) extend in parallel in a direction orthogonal to the plane of thedrawing sheet.

The bond (B1) between the manifold plate (75) and the microchannel plate(74) is sufficient to provide a watertight seal, but the bond (B1) doesnot have to provide a low thermal resistance. Accordingly, bondingmethods such as direct wafer bonding, fusion bonding, anodic bonding,glass frit bonding, solder bonding, polymer adhesive bonding, or anyother suitable bonding method may be used to join the microchannel andmanifold plates (74) and (75). Moreover, the bond (B2) between themicrochannel plate (74) and the chip (72) should be formed using a lowthermal resistance bond, to thereby allow sufficient heat conductionfrom the chip (72) to the microchannel plate (74). A low thermalresistance bond such as a metal joint, solder joint, or a filled thermaladhesive such as a Ag epoxy, or other joining means could be used, aslong as the bonding thickness is sufficiently thin and compatible withthe level of cooling flux required. It is desirable that the thermalresistance of the low thermal resistance bond be less than 0.2-C-cm²/W,or preferably, less than or equal to 0.1 C-cm²/W. Further, it isdesirable that the bond (B2) be reworkable, so that the microchannelcooler (71) can be removed from the chip (72), when necessary, to eitherreplace the individual cooler device (71) or replace the chip (72).Accordingly, a solder join can be reworked and if a solder layer is incontact with an Ag epoxy joint, it can also be reworked.

The dimensions of the manifold plate (75), such as thickness T₁, and thedimensions of the manifold structures, such as the depth d₁ of the fluidvias (v) and the depth d₂ of the manifold channels (C), can be the sameas those described above with respect to FIG. 4D. Moreover, recess depthd₃ of the microchannels (77) can be the same as described above withrespect to FIG. 5A˜B. However, in another exemplary embodiment of theinvention, the thickness T₂ of the microchannel plate (74) can bereduced (from the typical silicon wafer thickness of 0.75 mm) usingvarious methods to minimize the distance d₄ to reduce the temperaturedrop through the silicon thickness, thereby increasing thermalperformance of the package (70). For instance, in one embodiment, thethickness T₂ can be reduced from the typical thickness of 0.75 mm for a200 or 300 mm diameter silicon wafer such that the distance d₄ is about100 micron.

Various methods may be employed for constructing the package structure(70) of FIG. 7. In general, in one embodiment of the invention, themicrochannel plate (74) and the manifold chip (75) can be bonded to eachother and tested, and then thermally bonded to the back of the chip (72)with the microchannel plate (74) in contact with the back surface of thechip (72). More specifically, in one exemplary embodiment of theinvention, at the wafer level, a first wafer comprising a plurality ofmicrochannel plates formed therein can be bonded to a second wafercontaining a plurality of corresponding manifold plates. The bondedwafers can then be subjected to polishing, grinding, and/or lapping tothin down the substrate on which the microchannel plates are fabricated.Alternatively, the wafer containing the plurality of microchannel platescan first be thinned prior to bonding or dicing. With the two wafersbonded together, the wafers can be diced to separate out the individualmicrochannel cooler devices. Alternately, the wafers containing themicrochannel and manifold plates can be polished, diced, etc., and thenindividual microchannel cooler devices can be formed by bonding theindividual manifold and microchannel plates. Note that outsidedimensions of microchannel cooler (71) in FIG. 7 can be slightly greaterthan the outside dimensions of chip (72) so that microchannel cooler(71) extends beyond chip (72) slight on each side. Such a slightextension can improve the performance because the perimeter region wheremanifold plate (75) and microchannel plate (74) are joined togetherprovide reduced cooling compared to the interior regions of microchannelcooler (71). The slight extension allows the entire back surface of chip(72) to be in contact with the interior regions of microchannel cooler(71) which contain microchannels.

In another exemplary embodiment of the invention, the thermalperformance of the package structure (70) of FIG. 7 can be furtherimproved by thinning the substrate of the chip (72), in addition toreducing the thickness of the substrate material remaining beneath themicrochannels (77) in the microchannel plate (74). For example, as notedabove, the surface of the microchannel plate (74) which is bonded to thechip (72) can be polished to have only about 100 micron of Si presentbelow the deepest etched regions on the microchannel plate. Further, thethickness T₃ of the chip (72), e.g., processor chip, may be reduced toabout 0.3 mm from an initial Si wafer thickness of about 0.75 mm.

The exemplary microchannel cooler device embodiments described above,such as in FIG. 7, include integrated microchannel cooler devices thatare formed by joining separate manifold and microchannel plates. Inother embodiments of the invention, an integrated microchannel coolerdevice comprises a single plate that is constructed with bothmicrochannels and supply/return manifolds structures. For example, FIGS.8A and 8B are schematic diagrams illustrating an apparatus (80) forcooling a semiconductor chip according to another exemplary embodimentof the invention, which includes an integrated microchannel cooler (81)that is thermally bonded to the non-active surface of a semiconductorchip (82) which can be flip-chip bonded to a package substrate viasolder balls (83).

More specifically, FIG. 8A schematically illustrates a cross-sectionalview of an IC package structure (80) taken along a longitudinal linewhich extends in a direction orthogonal to a plurality of thermalmicrofins (84) and microchannels (85) in a heat exchanger zone of thecooler (81). Further, FIG. 8B schematically illustrates across-sectional view along a longitudinal line which (i) extends in adirection parallel to a zig-zag shaped fluid manifold structure formedat an end portion of the heat exchanger zone in the integrated cooler(81), and which (ii) passes through the center of each of a plurality offluid vias (v) formed on one side of the zig-zag shaped fluid manifoldstructure.

In other words, the integrated microchannel cooler device (81) frameworkdepicted in FIGS. 8A and 8B, combines the functions and structures ofthe microchannel plate and the manifold plate in one substrate layer.The exemplary microchannel cooler device (81) can be formed by etchingthe via patterns as discussed above to form the fluid vias (v) to adepth d₁ on one surface of the cooler substrate (81). Then, one or moredry etching steps could be used to form the manifold channels (C) andthe thermal microfins (84) and microchannels (85). If the manifoldchannels (C) are formed to have the same depth as the microchannels(85), i.e., d₂=d₃, the manifold channels (C) and microchannels (85) canbe formed with the same dry etching step. Alternately, the manifoldchannels and microchannels could be formed by two separate andindependent dry etch steps or a combination of two dry etch steps.

In the exemplary embodiment of FIGS. 8A and 8B, the manifold channels(C) are depicted as being deeper than the microchannels (85) (d₂>d₃). Insuch embodiment, two dry etch steps can be used to form deeper manifoldchannels (C) (which are deeper than the microchannels (85) by more thanthat which would result from RIE lag—wider features etch faster thannarrower features). With this configuration, the fabrication process canbe simpler and the performance can potentially be improved due to thedirect contact of the cooling fluid to the chip (82). Moreover, thethermal microfins (84) fins are joined to the chip (82) using a lowthermal resistant bond (B3). It is to be noted that with this design,the interior region of the microchannel cooler device (81) containingmicrochannels is smaller than the chip (82), because a perimeter regionis needed to seal the two together. Note that a hermetic bonding methodis needed in the perimeter region to form the seal.

FIGS. 9A˜9C are schematic perspective views of an integratedmicrochannel cooler device according to another exemplary embodiment ofthe invention. More specifically, as described above, FIG. 9A depicts athree-dimensional perspective view of a portion of manifold plate (90)having a fluid manifold (91), which comprises a manifold channel (92)formed in a zig-zag pattern and a plurality of fluid vias (v) that formopenings to the manifold channel (92). The channel segments (93) of themanifold channel (92) formed between the fluid vias (v) are tapered.

FIG. 9B depicts a three-dimensional perspective view of a portion of amicrochannel plate (94), which can be bonded to the manifold plate (90)of FIG. 9A to form an integrated microchannel cooler apparatus asdepicted in FIG. 9C. FIG. 9B is a perspective view of the microchannelplate (94) as viewed from the top where for clarity, the substrate isshown as semitransparent solid, illustrating a plurality of thermalmicrofins (95) formed on a bottom surface of the substrate in astaggered pattern. As compared to the exemplary embodiments abovewherein the microchannels are continuous in each heat exchanger zonebetween manifolds, the staggered microfin pattern depicted in FIG. 9Bcan be used to increase the heat transfer (compared to continuous fins)by having each fin segment shed the boundary layer, so a new boundarylayer is formed for each fin segment. This design also allows transversemixing (between channels); such a structure helps prevent catastrophicfailure due to channel clogging and provides an additional mechanism toimprove flow uniformity within the microfin region. Moreover, asdiscussed below, a staggered thermal microfin pattern can be used toprovide increased cooling capacity for chip “hot spot” regions.

FIG. 9C is depicts a perspective view of a portion of an integratedmicrochannel cooler module that is formed by bonding the manifold plate(90) of FIG. 9A and the microchannel plate (94) of FIG. 9B. Inparticular, FIG. 9C is a perspective view as viewed from the top surfaceof the microchannel plate substrate (94), which is shown assemitransparent solid for illustrative purposes, wherein the thermalmicrofins (95) pattern is discontinued in the regions R that are alignedalong the manifold channel (92).

In other exemplary embodiments of the invention, microchannel coolingapparatus include fluid distribution manifolds for SCM and MCM packages,which are connected to separate integrated microchannel cooler devicesthat are bonded to the back surfaces of chips that are flip-chip bondedto a substrate, for delivering coolant fluid to/from integratedmicrochannel cooler devices. High performance chips, e.g., processors,are typically mounted face down to a packaging substrate, made from aceramic or organic material and containing multiple wiring layers, usingan area array of microsolder balls such as C4's. In a multichip module(MCM), many chips are mounted on a common substrate and with a singlechip module (SCM) only one chip is attached to the substrate. Theceramic substrate provides a space transformation between the fine pitch(˜200 micron) C4 s and the more coarse pitch electrical connectionsbetween the 1^(st) level package substrate and the printed circuitboard, or 2^(nd) level package, which are about 1 mm apart. One commonmeans of providing electrical connection between a 1^(st) and a 2^(nd)level package is a land grid array (LGA) which requires a significantcompression force to be applied to actuate the LGA.

FIGS. 10 and 11 are schematic diagrams illustrating fluid distributionmanifolds according to exemplary embodiments of the invention, which canbe implemented for SCM and MCM chip packages. The exemplary fluiddistribution manifolds are designed in a manner to minimize overallsystem pressure drop by using variable cross-sectional fluidsupply/return channels for delivering coolant fluid to/from integratedmicrochannel cooler devices. Moreover, exemplary embodiments of theinvention implement connection mechanisms that provide mechanicaldecoupling between the fluid distribution manifolds and the integratedmicrochannel cooler devices to prevent excess stress on the C4's whichattach the chips to the package substrate. More specifically, forpurposes of providing mechanical compliance when a fluid distributionmanifold is secured to a microchannel cooler, a mechanically compliantgasket/seal is provided between the fluid distribution manifold and amicrochannel cooler to seal the junction between such components. Themechanically compliant gasket comprises any suitable compressiblematerial, such as elastomer, or any other suitable material that can becompress when coupling the coolant deliver manifold to the microchannelstructure may be securely made while tolerating differences in height ofthe integrated circuit chips, and without requiring large pressureswhich can damage the chips. The compliant gasket material may also beadhered or bonded to the microchannel cooler and the fluid distributionmanifold so that it need not be maintained in a compressed state to forma fluid seal.

By way of example, FIG. 10 is a schematic plan view of a fluiddistribution manifold device according to an exemplary embodiment of theinvention, which can be used with an integrated microchannel coolerdevice formed with the above-described exemplary manifold plate (40) fora single chip module (SCM). More specifically, FIG. 10 illustrates anexemplary fluid distribution manifold (100) comprising a housing (101)having a fluid return manifold (102) and fluid supply manifold (103) cutor formed therein. The fluid return manifold (102) comprises a pluralityof flow channels indicated by the horizontal cross-hatched regions, andthe fluid supply manifold (103) comprises a plurality of flow channelsindicated by the vertical cross-hatched regions. Further, circularregions (104) and (105) indicate where output and input ports would bemade in a cover plate (not shown) secured to the housing (101) toprovide the fluid supply/return connections to the fluid distributionmanifold (100).

The manifold (100) includes a plurality of elongated rectangularopenings (106) and (107) on the bottom surface of the housing (101),which are coupled to fluid vias (v) of corresponding manifolds (Mi) onthe manifold plate (40) in FIG. 4C with a mechanically compliant gasket.For example, in the exemplary embodiment, the rectangular openings (107)are aligned with and coupled to the fluid vias of the input manifoldsM2, M4, and M6 to supply coolant fluid into the microchannel coolerdevice and the rectangular openings (106) are aligned with and coupledto the fluid vias of the output manifolds M1, M3, M5 and M7 forreceiving heated fluid that is returned from the microchannel coolerdevice.

Moreover, as depicted in FIG. 10, the manifolds (102) and (103) areformed with variable cross section channels to maintain the velocity ofthe fluid flow near constant and reduce dynamic pressure drop. Forinstance, the cross-sectional area of the flow channel of the supplymanifold (103) that is aligned with the inlet port (105) is tapered toprovide uniform distribution of the input coolant fluid to each of theflow channels which feed the rectangular openings (107). Further, theflow channels which feed the rectangular openings (107) are also taperedto reduce the cross-section area to uniformly supply coolant fluid tothe input fluid vias along the input manifolds of the integratedmicrochannel cooler connected thereto. Similarly, the various flowchannels that form the return manifold (102) are designed with variablecross-sectional area to reduce dynamic pressure drops for the returnfluid received from the output manifolds of the integrated microchannelcooler attached thereto. For instance, the cross-sectional area of theflow channel of the supply manifold (102) that is aligned with theoutput port (105) is tapered to provide uniform redistribution of theoutput coolant fluid that flows from each flow channel having therectangular openings (106). Moreover, the flow channels which receivereturn fluid from the rectangular openings (106) are also tapered toreduce the cross-section area to provide a uniform flow andredistribution of coolant fluid that is received from the outlet fluidvias along the output manifolds of the integrated microchannel coolerconnected thereto.

It is to be appreciated that the cross-sectional areas of thesupply/return manifold segments can also be varied by varying the recessdepths of such segments, in addition to or in lieu of, varying thechannel widths such as shown in FIG. 10. In all instances, the area ofthe flow channels are decreased sufficiently to reduce the dynamicpressure drop by maintaining the velocity of the coolant fluidsubstantially, or very close to, constant along the flow channels in thefluid distribution manifold device (100). Moreover, although notspecifically shown, a further reduction ins pressure drop can beobtained by rounding the corners of the flow channels of the input andoutput manifolds (102) and (103) to reduce the resistance to flow.

The fluid distribution manifold can be formed of any suitable corrosionresistant material, such as copper or plastic or other material, inwhich the flow channels of the input and output manifolds can be milled,drilled, molded, or otherwise formed in a block of such material. Thefluid distribution manifold (100) should be of sufficient dimensionswith larger variable cross-sections to properly feed inlet and outletmanifolds of the integrated microchannels cooler device connectedthereto. This particular larger variable cross-section manifold can notbe machined into the manifold plate, mainly because of geometricalconstraints which require the additional cross-section area to be formedwith higher vertical dimensions, which can not be achieved using a thinplate such as a silicon wafer.

FIG. 11 is a schematic plan view of a fluid distribution manifold deviceaccording to another exemplary embodiment of the invention. Inparticular, FIG. 11 depicts a common fluid distribution manifold (110)which can be implemented with a multi-chip module (MCM) that comprisesan array of four flip-chip bonded chips, wherein each chip has aseparate integrated microchannel cooler device attached thereto, whichis formed with the exemplary manifold plate (40) as depicted in FIG. 4C.The exemplary fluid distribution manifold (110) comprises a housing(111) having two fluid supply manifolds (112) and (113), which aresupplied with coolant fluid from respective inlets (114) and (115)formed in a cover plate (not shown), as well as two fluid returnmanifolds (116) and (117), which output fluid to respective outlet ports(118) and (119) formed in the manifold cover. The exemplary fluiddistribution manifold (110) comprises four manifold sections (A, B, Cand D), which are similar in structure to the fluid distributionmanifold structure (100) of FIG. 10.

The fluid supply manifolds (112) and (113) comprise a plurality of flowchannels indicated by the vertical cross-hatched areas, which are cut orformed in the housing (111). The fluid supply manifold (113) suppliescoolant fluid to 2 integrated microchannel coolers connected to manifoldsections A and B and the fluid supply manifold (112) supplies coolantfluid to 2 integrated microchannel coolers connected to manifoldsections C and D. More specifically, the fluid supply manifold (113)comprises flow channel regions having a plurality of rectangularopenings (120 a) that are aligned with the fluid vias of correspondinginput manifolds of a first microchannel cooler device coupled to themanifold section A, as well as flow channel regions having a pluralityof rectangular openings (120 b) that are aligned with the fluid vias ofcorresponding input manifolds of second microchannel cooler devicecoupled to the manifold section B. Similarly, the fluid supply manifold(112) comprises flow channel regions having a plurality of rectangularopenings (120 c) that are aligned with the fluid vias of correspondinginput manifolds of a third microchannel cooler device coupled to themanifold section C, as well as flow channel regions having a pluralityof rectangular openings (120 d) that are aligned with the fluid vias ofcorresponding input manifolds of a fourth microchannel cooler devicecoupled to the manifold section D.

The fluid return manifolds (116) and (117) comprise a plurality of flowchannels indicated by the horizontal cross-hatched areas, which are cutor formed in the housing (111). The fluid return manifold (116) receivescoolant fluid returned from 2 integrated microchannel coolers connectedto manifold sections A and C and the fluid return manifold (117)receives coolant fluid returned from two integrated microchannel coolersconnected to manifold sections B and D. More specifically, the fluidreturn manifold (116) comprises flow channel regions having a pluralityof rectangular openings (121 a) that are aligned with the fluid vias ofcorresponding output manifolds of the first microchannel cooler devicecoupled to the manifold section A, as well as flow channel regionshaving a plurality of rectangular openings (121 c) that are aligned withthe fluid vias of corresponding output manifolds of the thirdmicrochannel cooler device coupled to the manifold section C. Similarly,the fluid return manifold (117) comprises flow channel regions having aplurality of rectangular openings (121 b) that are aligned with thefluid vias of corresponding output manifolds of the second microchannelcooler device coupled to the manifold section B, as well as flow channelregions having a plurality of rectangular openings (121 d) that arealigned with the fluid vias of corresponding output manifolds of thefourth microchannel cooler device coupled to the manifold section D.

Therefore, as described above, a fluid distribution system according toan exemplary embodiment of the invention, which can be used forimplementing a microchannel cooling apparatus, comprises a fluiddistribution manifold block (e.g., 100 or 110) coupled with a compliantgasket to a manifold plate (e.g., manifold plate (40)) of one or moremicrochannel cooler devices, where at least the distribution manifoldblock and the manifold plate have variable cross-sections (i.e. tapered)flow channels. The compliant gasket may or may not contain variablecross-section flow channels.

In other exemplary embodiments of the invention, various methods may beimplemented for custom designing microchannel cooler devices to providelocalized cooling capacity for one or more “hot spot” regions of a chip(regions with higher than average power density). More specifically, forchips having a non-uniform power density distribution (non-uniform powermap), an integrated microchannel cooler device according to theinvention can be custom designed by providing manifold and microchannelstructures, patterns, arrangements, etc., which enable increasedlocalized cooling capacity for chip hot spots. The manner in which suchintegrated microchannel cooler devices can be custom designed will varydepending on factors such as the size, magnitude, and/or number of hotspot regions of a chip. Various exemplary methods according to theinvention for designing microchannel cooler devices to provide increasedlocalized cooling capacity for chip hot spot regions will now bediscussed with reference to FIGS. 12-16 and 17A˜B).

FIG. 12 schematically illustrates a method for designing an integratedmicrochannel cooler device to provide a locally increased coolingcapacity for a “hot spot” region of a chip, according to one exemplaryembodiment of the invention. In general, FIG. 12 illustrates anexemplary design method in which an integrated microchannel coolerdevice can be designed with a uniform structure that provides uniformcooling which is sufficient for an expected average power density of achip, while at the same time providing an increased localized coolingcapacity for a “hot spot” region of a chip. More specifically, FIG. 12depicts an exemplary microchannel plate (125) having a uniform,multi-zone heat exchanger structure (similar to that shown in FIG. 5B),wherein a region (126) corresponds to a “hot spot” region of a chip. Asdiscussed above, the exemplary uniform microchannel framework (uniformmicrochannel patterns and evenly spaced I/O manifolds) enables a uniformfluid flow across all heat exchanger zones and provides uniform coolingover the surface of the chip.

Assuming the microchannel plate (125) is designed to provide uniformcooling capability for the expected average power density of the chip,as depicted in FIG. 12, an increased localized cooling for the hot spotregion (126) of the chip is obtained by designing the microchannel plate(125) to have an input fluid manifold (127) that is aligned to the hotspot region (126) of the chip. The exemplary method of FIG. 12 can beused to provide increased localized cooling of the “hot spot” region(126) of the chip when, for instance, the “hot spot” region (126) has arelatively small area with a modest increased power density as comparedto the average power density of the chip for which the microchannelcooler is designed. This is because in a typical microchannel coolerdesign, there can be a significant increase in fluid temperature, up toabout 10° C. depending on the cooling fluid and the configuration, alongthe length of the microchannels. Therefore, with the exemplary method ofFIG. 12, the “hot spot” temperature can be reduced by approximately theamount of temperature gained by the fluid flowing along the channels. Inaddition, the exemplary method of FIG. 12 provides an arrangement inwhich the central portion/axis of the hot spot region (126) is alignedwith the entrance of microchannels where the local heat transfercoefficient is higher than in the rest of the channel lengths, whicheffectively provide increased localized cooling for the hot spot (126).

In general, it should be noted that a uniform microchannel coolerstructure providing uniform cooling capability, such as depicted inFIGS. 12 and 5B, may be used for cooling a chip having a “hot spot”region, whereby the microchannel cooler is designed to provide uniformcooling for an expected higher than average power density of the “hotspot”. However, this “uniform” design method may be inefficient forcooling a chips with “hot spot” regions because the required water flowsand pressure drops are increased over an optimum design. Indeed, a “highperformance” microchannel patterns (e.g., fine-pitched microchannels, ormicrochannels defined by staggered or interrupted microfins (e.g., FIGS.17A˜B), with a high fluid flow) may be needed to adequately cool a “hotspot”, but such patterns result in a large pressure drops.

Therefore, a more optimum microchannel cooler design would be to provide“high performance” microchannel patterns for chip “hot spots” having agreater than average power density, while using a lower performancemicrochannel pattern (e.g., use a less fine microchannel pitch and alower flow rate design) for the regions of the chip with reduced powerdensities (e.g., average power density). With such methods, thestructure of the microchannel cooler device is not “uniform”, butcontains regions which under the same operating conditions (i.e., sametotal pressure drop for each heat exchanger section) as surroundingregions provide, are able to cool higher power densities and are alignedwith hot spot regions on the chip. In other words, an integratedmicrochannel cooler device can be custom designed for a given chip basedon a power map (power density distribution) of the chip by varying themicrochannel performance in the same and/or different heat exchangerzones to match the (non-uniform) power map of the chip. Various methodsaccording to the invention in which the microchannel performance isvaried to provide increased local cooling capacity for chips havinglarge hot spots and/or hot spots with a significantly higher powerdensity as compared to the average power density of the chip, will benow be described with reference to the exemplary embodiments of FIGS.13-16 and 17A˜B.

For example, FIG. 13 schematically illustrates a method for providing alocally increased cooling capacity for a hot spot region of a chipaccording to another exemplary embodiment of the invention. Inparticular, FIG. 13 depicts an exemplary microchannel plate (130) havinga multi-zone heat exchange structure similar to that shown in FIG. 12,wherein a region (131) (hot spot region) corresponds to a “hot spot” ofa chip. However, in the exemplary embodiment of FIG. 13, the hot spot(131) of the chip is assumed to have a significantly higher powerdensity as compared to the average power density of the chip to becooled, which can render the method of FIG. 12 insufficient for coolingthe hot spot by merely aligning an input manifold to the hot spot.Accordingly, in the exemplary embodiment of FIG. 13, increased localizedcooling for the hot spot region (131) can be obtained by aligning aninput manifold (132) with the hot spot region (131), as well as changingthe microchannel pattern in an area surrounding the portion of the inputmanifold (132) corresponding to the hot spot region (131) by usinginterrupted or staggered fins (as shown schematically in the exemplaryembodiments of FIG. 17A or 17B).

In particular, FIG. 17A schematically illustrates an interruptedmicrofin pattern (170) comprising a plurality of rows of parallelmicrofins (171, 172, 173) that are separated by pitch P. Each row ofmicrofins (171, 172, 173) comprises a plurality of relatively longmicrofin structures (174) that are separated by small gaps (G1)(interruptions) between the microfins (174) along the row, wherein thegaps (G1) of adjacent rows are staggered. The interrupted microfinpattern (170) defines relatively long microchannels that enable crossmixing of fluid between the microchannels.

On the other hand, FIG. 17B schematically illustrates a staggeredmicrofin pattern (175) comprising a plurality of rows of parallelmicrofins (176, 177, 178, 179, 180), wherein every other row (e.g., row176 and 178) are separated by the same pitch P (as in FIG. 17A). Eachrow of microfins (176, 177, 178, 179, 180) comprises relatively shortmicrofin structures (181) with gaps (G2) (interruptions) between themicrofins (181) along that row, wherein the gaps (G2) of adjacent rowsare staggered. In the exemplary embodiment of FIG. 17B, the length ofthe microfin structures (181) and gaps (G2) are relatively the same. Theexemplary microfin pattern depicted in FIG. 9B is formed with astaggered pattern similar to that depicted in FIG. 17B.

Referring back to FIG. 13, a high performance microchannel patterncomprising a staggered microfin pattern (as shown in FIG. 17B) can beused the hot spot region (131) to achieve a 2× increase in the heattransfer coefficient. The increase in the heat transfer rate is expectedfor two reasons. First, each microfin segment is too short to yielddeveloped flow and, consequently, each microfin segment behaves like ashort channel with expected higher local heat transfer coefficient andsome fractional increase in pressure drop. In addition, the staggeredarray delivers energy to the fluid stream centerline, while preservingthe fin to fin pitch of the continuous microfin patterns in thesurrounding regions, thus behaving like a narrower channel thermally.Advantageously, the use of staggered or interrupted fins in the hot spotregion (131) will provide a local increase in the heat transfercoefficient. But since the modified fin pattern is in parallel withregions of continuous fins, the flow can be reduced because staggered orinterrupted fins cause an increase in the pressure drop along themicrochannel, as compared to the regions of continuous fins. Suchreduction in flow may be acceptable for more significant increases inpower density when limited to small sections of the chip representingonly a fairly modest fraction of the total power for which themicrochannel cooler is designed. It is desirable to limit the reductionof flow per unit area perpendicular to the channels in the regionscontaining the modified fin pattern to less than about ½ of that in theregions containing the normal fin pattern. Alternatively, it isdesirable to limit the reduction of the fluid velocity in the regionscontaining the modified fin pattern to less than about ½ of that in theregions containing the normal fin pattern.

However, as noted above, it is preferable for all the heat exchangerzones to be connected in “parallel” which means that they should all bedesigned to operate with the same pressure drop between the inlet andoutlet manifolds and the manifolds should be designed with variablecross-sectional areas to provide uniform fluid flow across the heatexchanger sections.

FIG. 14 schematically illustrates a method for providing a locallyincreased cooling capacity for a hot spot region of a chip according toyet another exemplary embodiment of the invention. In particular, FIG.14 depicts an exemplary microchannel plate (140) having a 6-zone heatexchange structure, wherein a region (141) (hot spot region) correspondsto a “hot spot” of a chip. Similar to the method of FIG. 13, localizedcooling is obtained by aligning an input manifold (142) with the hotspot region (141) and forming a high performance microchannel pattern(e.g., an interrupted or staggered microfin pattern) for the hot spotregion (141). However, FIG. 14 further depicts a method for providinglocalized increased cooling by moving/rerouting portions (143 a) and(144 a) of respective output manifolds (143) and (144) toward the hotspot region (141) aligned with the input manifold (142). This methodeffectively reduces the channel length of the microchannels in theregions of the heat exchanger zones between the portion of the inputmanifold (142) aligned to the hot spot region (141) and the reroutedportions (143 a) and (144 a) of output manifolds (143) and (144), suchthat the pressure drop is the regions of the heat exchanger zones withthe shortened channel lengths is substantially the same as the pressuredrop in the other regions of such heat exchanger zones wherein themicrochannels are longer and continuous (not interrupted or staggered).

With the exemplary localized cooling method of FIG. 14, assuming thenumber of heat exchanger zones is constant, the length of themicrochannels in the regions of the heat exchanger zones between themanifold portion (144 a) and input manifold (145) and between themanifold portion (143 a) and input manifold (146) will be increased,thereby reducing the flow and hence cooling in these regions. However,this may be acceptable depending on the power map of the chip.

FIG. 15 schematically illustrates a method for providing a locallyincreased cooling capacity for a hot spot region of a chip according toanother exemplary embodiment of the invention. In particular, FIG. 15depicts an exemplary microchannel plate (150) generally having a 6-zoneheat exchange structure, wherein a region (151) (hot spot region)corresponds to a “hot spot” of a chip. FIG. 15 depicts an exemplarymicrochannel plate (150) that is designed to provide increased coolingcapacity for a relatively large hot spot of a chip, wherein additionalmanifolds are formed in the region (151) so that the channel lengths canbe reduced locally. In the exemplary embodiment of FIG. 15, six heatexchanger zones are defined for cooling those regions of the chip withaverage power density. However, in the hot spot region (151), additionalmanifolds are formed such that six heat exchanger zones are defined forthe hot spot alone.

FIG. 16 schematically illustrates a method for providing a locallyincreased cooling capacity for hot spot regions of a chip according toyet another exemplary embodiment of the invention. More specifically,FIG. 16 depicts an exemplary microchannel plate (160) having regions(161) and (162) that correspond to two relatively large “hot spots” of achip. In the exemplary embodiment of FIG. 16, the power density isassumed to be very high in the hot spots of the chip and relativelysmall in the remaining region of the chip. The microchannel plate (160)comprises two heat exchanger zones (163) and (164), wherein the heatexchanger zone (163) is designed to cool the higher power density regionof the chip corresponding to hot spot regions (161) and (162), andwherein the heat exchanger zone (164) is designed to cool the lowerpower density regions of the chip. To provide increased cooling capacityfor the hot spot regions of the chip while maintaining the pressure dropacross the heat exchanger zones (163) and (164) substantially the same,the heat exchanger zone (163) is designed with relatively shorter andfinely-pitched microchannels, whereas the heat exchanger zone (164) isdesigned with relatively longer and coarsely-pitched microchannels.

In another exemplary embodiment, in the shorter heat exchanger zone(163), two different microchannel patterns can be formed. Morespecifically, by way of example, a high performance microchannel designcan be used within a region (165) bounded by the dot-dashed lines, whichmay result in a higher pressure drop per unit length, whereas a lowerperformance microchannel design can be used in the area of the heatexchanger zone (163) that surrounds the region (165). Moreover, in theexemplary embodiment of FIG. 16, the total length of the microchannelsin the high performance region (165) and the total length of thesurrounding lower performance microchannel region is the same for allthe individual microchannels in the shorter heat exchanger zone (163).The high performance microchannel region (165) may include microchannelsthat are patterned, structured or arranged in one of various ways. Forinstance, the region (165) may include finer-pitched microchannels, ormicrofins that are formed with staggered or interrupted patterns (as inFIGS. 17A and 17B). Alternatively, the microchannels in region (165) mayhave the same pitch but reduced channel width.

In other exemplary embodiments of the invention, increased local coolingcapability can be attained by designing the microfins to extend into themanifold region (i.e., extend into the recessed regions (R)), althoughsuch methods can result in an increased pressure drop depending on howfar the microfins extend into the recessed region. In anotherembodiment, the thermal microfins can be designed such that every otherfin has a longer length relative to its adjacent fin, wherein the extralength places the fin endings directly under the inlet/outlet fluid viason the manifold plate. With this embodiment, half of the microfins canbe used to increase the conduction paths under the inlet fluid vias andincrease conduction cooling on areas with fluid stagnation points underthe outlet fluid vias, thus locally increasing the overall coolingcapability in the manifold regions, although there is a modest increasein the pressure drop.

Although exemplary embodiments have been described herein with referenceto the accompanying drawings, it is to be understood that the presentsystem and method is not limited to those precise embodiments, and thatvarious other changes and modifications may be affected therein by oneskilled in the art without departing from the scope or spirit of theinvention. All such changes and modifications are intended to beincluded within the scope of the invention as defined by the appendedclaims.

1. An integrated microchannel cooler device for cooling an IC(integrated circuit) chip having a non-uniform power map, the integratedmicrochannel cooler device comprising: a plurality of alternating inputand output manifolds that extend in a same direction within theintegrated cooler device; and a plurality of heat exchanger zones,wherein each heat exchanger zone comprises a plurality of thermalmicrofins which define a microchannel pattern of microchannels whichextend between an adjacent input and output manifold to provide fluidflow paths between the adjacent input and output manifold, wherein themicrochannel pattern of one or more of the heat exchanger zones isvaried to provide a heat transfer performance that corresponds to anexpected power map of the IC chip; and wherein the input and outputmanifolds and microchannel patterns of the heat exchanger zones arestructured to provide an average fluid velocity in a region of a heatexchanger zone that corresponds to an expected hot spot region of the ICchip, which is substantially the same as, or at least within about 50%of, an average fluid velocity in other regions of the heat exchangerzone that do not correspond to an expected hot spot region of the ICchip.
 2. The integrated microchannel cooler device of claim 1, whereinat least one input manifold of the integrated microchannel cooler deviceis arranged to align with an expected hot spot region of the IC chip. 3.The integrated microchannel cooler device of claim 1, wherein themicrochannel pattern of one or more of the heat exchanger zones isvaried locally to provide a heat transfer performance that correspondsto local variations of the expected power map of the IC chip.
 4. Theintegrated microchannel cooler device of claim 3, at least one heatexchanger zone comprises a first pattern of microchannels that providesa heat transfer performance sufficient for an expected average powerdensity of the IC chip and a second pattern of microchannels that isdisposed to correspond to an expected hot spot region of the IC chip,wherein the second pattern of microchannels provides a heat transferperformance sufficient for an expected greater than average powerdensity of the hot spot.
 5. The integrated microchannel cooler device ofclaim 4, wherein the first pattern of microchannels comprises continuousmicrochannels and wherein the second pattern of microchannels comprisesa pattern of staggered or interrupted microfins.
 6. The integratedmicrochannel cooler device of claim 4, wherein the first pattern ofmicrochannels comprises continuous parallel microchannels spaced with afirst pitch and wherein the second pattern of microchannels comprisescontinuous parallel microchannels spaced with a second pitch that issmaller than the first pitch, and more preferably greater than or equalto about one-half the first pitch.
 7. The integrated microchannel coolerdevice of claim 4, wherein the first pattern of microchannels comprisesa pattern of staggered or interrupted microfins spaced with a firstpitch and wherein the second pattern of microchannels comprises apattern of staggered or interrupted microfins spaced with a secondpitch.
 8. The integrated microchannel cooler device of claim 4, whereinthe first and second pattern of microchannels of the heat exchanger zoneare arranged in series between an adjacent input and output manifold. 9.The integrated microchannel cooler device of claim 8, wherein the firstpattern of microchannels comprises regions where a flow per unit widthperpendicular to the first and second pattern of microchannels in seriesis not reduced by more than ½ as compared to the first pattern ofmicrochannels alone.
 10. The integrated microchannel cooler device ofclaim 1, wherein the microchannel pattern of one or more of the heatexchanger zones is varied by using a same first microchannel pattern forone or more heat exchanger zones, which provides a heat transferperformance sufficient for an expected average power density of the ICchip, and using at least one second microchannel pattern in a heatexchanger zone that corresponds to an expected hot spot region of the ICchip, which provides an increased heat transfer performance sufficientfor an expected greater than average power density of the chip.
 11. Theintegrated microchannel cooler device of claim 10, wherein the firstmicrochannel pattern comprises continuous microchannels which have afirst length that extends between an input and output manifold, andwhich are spaced apart with a first pitch, and wherein the at least onesecond microchannel pattern comprises continuous microchannels whichhave a second length that extends between an input and output manifold,and which are spaced apart with a second pitch, wherein the first lengthand pitch is greater than the second length and pitch.
 12. Theintegrated microchannel cooler device of claim 1, wherein themicrochannel pattern of one or more of the heat exchanger zones isvaried by using a same first microchannel pattern for one or more heatexchanger zones, which provides a heat transfer performance sufficientfor an expected average power density of the IC chip, and using at leasta second and a third microchannel pattern in a heat exchanger zone thatcorresponds to an expected hot spot region of the IC chip, which providean increased heat transfer performance sufficient of an expected greaterthan average power density of the chip.
 13. The integrated microchannelcooler device of claim 12, wherein the first microchannel patterncomprises continuous microchannels which have a first length thatextends between an input and output manifold, and which are spaced apartwith a first pitch, and wherein the at least a second and thirdmicrochannel patterns are disposed in series over the heat exchangerzone that corresponds to the expected hot spot region of the IC chip,and wherein a total proportion of the at least second and thirdmicrochannel pattern is substantially the same for any given channelover the heat exchanger zone.
 14. The integrated microchannel coolerdevice of claim 13, wherein the at least second microchannel pattern isdisposed to substantially align with the expected hot spot region of theIC chip and provide a second heat transfer performance sufficient for anexpected power density of hot spot region of the IC chip and wherein thethird microchannel pattern is disposed in areas of the heat exchangerzone surrounding the second microchannel pattern and provides a thirdheat transfer performance which is less than the second heat transferperformance, but greater than a first heat transfer performance providedby the first microchannel pattern.
 15. An apparatus for cooling anelectronic device, comprising: an integrated microchannel cooler devicecomprising a plurality of alternating input and output manifoldsextending in a same direction, wherein at least one heat exchanger zoneis defined between each adjacent input and output manifold, wherein eachheat exchanger zone comprises a plurality of thermal microfins whichdefine microchannels that provide a fluid flow path between adjacentmanifolds; and an IC (integrated circuit) chip having a non-activesurface which is thermally bonded to the integrated microchannel coolerdevice, wherein the IC chip and integrated microchannel cooler arebonded such that an input manifold of the integrated microchannel cooleris aligned with a hot spot region of the IC chip.
 16. The apparatus ofclaim 15, wherein said input manifold is aligned with a central point ofthe hot spot region.
 17. The apparatus of claim 15, wherein a distancebetween adjacent manifolds are reduced in a region aligned to the hotspot region and the flow per unit width perpendicular to themicrochannels does not vary by more than ½ in different regions of theheat exchanger zone.
 18. The apparatus of claim 15, wherein a number ofheat exchanger regions of the integrated microchannel cooler deviceacross the IC chip is varied such that the number of heat exchangerzones in the portion of the integrated microchannel cooler device thatis aligned to the hot spot region of the IC chip is increased to provideincreased cooling for the hot spot region.